01 - In a large mixing bowl or stand mixer fitted with a dough hook, combine the flour, sugar, yeast, and salt. Whisk the warm milk and egg together, then pour into the dry ingredients. Mix until a shaggy dough begins to form. Add the softened butter and knead for 8 to 10 minutes until the dough is smooth, elastic, and slightly tacky. Cover the bowl with a damp towel or plastic wrap and let the dough rise in a warm spot for 1 hour, or until doubled in size.
02 - Place 200 g of room-temperature butter between two sheets of parchment paper. Using a rolling pin, shape the butter into a rectangle approximately 8 x 10 inches. Transfer to the refrigerator and chill until firm but still pliable, about 15 to 20 minutes.
03 - On a lightly floured surface, roll the risen dough into a large rectangle approximately 16 x 12 inches. Place the chilled butter layer over one half of the dough, then fold the other half on top to enclose the butter. Gently roll the dough out again to its original size and fold it into thirds like a letter. Wrap in plastic and refrigerate for 20 minutes. Repeat the rolling and folding process two more times, chilling the dough for 20 minutes between each fold to keep the butter cold.
04 - Roll the laminated dough out once more into a rectangle approximately 16 x 12 inches. Trim the edges with a sharp knife or pizza cutter for clean, even lines. Cut the dough lengthwise into 12 equal strips. If using a filling, spread a thin, even layer of chocolate spread, jam, or your chosen filling along each strip.
05 - Roll each strip tightly from end to end into a compact spiral. Using a sharp knife, cut each spiral in half lengthwise to expose the flaky inner layers. Twist each half into a loose knot and place it cut-side up into a generously greased 12-cavity muffin tin.
06 - Cover the muffin tin loosely with a damp towel or oiled plastic wrap. Allow the shaped cruffins to rise in a warm, draft-free area for 45 to 60 minutes until noticeably puffy and nearly doubled.
07 - Preheat the oven to 400°F (200°C). Bake the cruffins on the center rack for 20 to 25 minutes, rotating the tin halfway through, until the tops are a deep golden brown and the layers are visibly flaky.
08 - Remove the cruffins from the oven and let them cool in the tin for 3 to 4 minutes. While still warm, brush the tops lightly with melted butter and roll them in cinnamon sugar if desired. Transfer to a wire cooling rack. Serve as-is or pipe lemon curd, Nutella, or pastry cream into the center for an extra indulgent treat.